Download Section 8-5 Day 2: Mixed Methods

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Section 8-5 Day 2
Determining the Equation of a Line
The 3 forms of an equation of a line are:
Slope-Intercept Form
Point-Slope Form
Standard Form
y – y1 = m(x – x1)
Ax + By = C
m = slope
m = slope
slope = 
b = y-intercept
(x1, y1) given point
y-intercept =
* use given slope and y-intercept
* use given a point and slope
or given 2 points
*** NEVER start here
y = mx + b
A
B
C
B
To write the equation of line:
Pick the form that matches the information you are given { y  mx  b or y–y1 = m(x–x1) }
Substitute given information into the corresponding equation
Solve equation for the appropriate form in the directions
Given a graph:
o Find your y-intercept (b) and slope (m)
 Given two points:
o Find the slope
o Pick a point
o Use point-slope to write the equation of the line
 Given intercepts:
o Write the intercepts as ordered pairs
o Find the slope
o Substitute slope and y-intercept into y  mx  b
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Write an equation of the line in slope-intercept form of each line described.
1. slope 2; y-intercept 15
1
2
2. slope  ; y-intercept
3
2
3. slope –3, (–1, 2)
Write an equation of the line in standard-form form of each line described.
4. slope
2
; x-intercept –3
3
7. y-intercept = 3,
x-intercept = – 4
5. slope 0 , through (1, –4)
6. (4, –3) and (3, –6)
8. horizontal line
through (–5, –12)
9. vertical line
through (9, –15)
Write an equation of the line in slope-intercept form of each line graphed.
10.
11.
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13.
12.
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14.
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15.
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